The present invention relates to double tapered rollers of a scroll thrust bearings, and more particularly to a conical surface shape of double tapered rollers used as rolling elements in a scroll thrust bearing preferably employed, for example, in a thrust force support structure in a scroll type compressor.
The scroll type compressor is a kind of rotary compressors, and fluid compression is continuous, and as compared with the conventional reciprocating compressors, torque fluctuations and vibrations are small and high speed operation is possible, and hence it is recently applied widely.
This kind of compressor has a thrust force support structure for enabling scroll driving. This support structure is a so-called built-in type integrally incorporated in the compressor, but forms a kind of thrust bearing, and a bearing known as ball coupling used in such position has been already known as an independent machine element.
Anyway, as the rolling elements, balls such as steel balls are used, and such balls are supported in point contact state, and are hence small in load capacity and inferior in durability, and they cannot withstand long-term use in the conditions of high speed and high load, and have problems in the service life.
In this regard, as shown in FIG. 4, a scroll type compressor having plural double tapered rolling elements (double tapered rollers) as thrust force support structure has been proposed.
The scroll structure of the compressor is characterized, as shown in the drawing, by fixing a fixed scroll member (c) having a volute body (b) in a housing (a), supporting a swirl scroll member (e) having a volute body (d) engaged with the volute body (b) so as to be free to swirl or revolve by means of a thrust force support structure (f), and driving and coupling the swirl scroll member (e) to a drive source not shown through a drive shaft (h) having a crankpin (g).
This support structure (f) is formed as a kind of thrust bearing as mentioned above, and a plurality of double tapered rollers R, R, . . . , are interposed between a pair of parallel bearing races (i), (j) so as to be free to roll. The double tapered rollers R are held in a pair of pockets provided oppositely to the bearing races (i) and (j), respectively (see, for example, Japanese Laid-open Patent No. 62-274113, Japanese Laid-open Patent No. 7-119741).
By rotary driving of the crankpin (g), the swirl scroll member (e) swirls or rotates without revolving on the fixed scroll member (c), and the fluid gas sucked in from a suction port (not shown) is compressed in a compression chamber formed between the volute bodies (b, d), and discharged from a discharge port (not shown)
In this case, the double tapered rollers R captured in the pockets of bearing races (i, j) make rolling motions in the pockets to assure relative and smooth swirl of the both bearing races (i, j), and arrest relative rotation of both bearing races (i, j) (rotation of swirl scroll member (e)).
In the thrust force support structure (f) using such double tapered rollers R, R, . . . , as compared with the conventional rolling elements made of spherical bodies, the durability is improved by far, and it is possible to withstand high seed and heavy load for a longer period.
In spite of such excellent durability, the assembling and manufacturing technology of such thrust force support structure (f) is not established, and, in addition, the double tapered roller R itself has a special shape as compared with other conventional rolling elements, and it is not completed sufficiently as the rolling element for bearing. Hence, the scroll type compressor having the thrust force support structure (f) using double tapered rollers R is not put in practical use yet.
That is, the general shape of double tapered roller R, as shown in FIG. 5(a), has a pair of conical or tapered surfaces Ra, Rb, and corners of double tapered roller R (that is, both ends of generators of conical surfaces Ra, Rb) Rc, Rd are formed in a round shape, but in such shape, an edge load due to load at both ends of the section straight line (generator) is generated, and the contact stress with the bearing races (i,j) becomes excessive (see FIG. 5(b)).
For example, in FIG. 5(a), when the length L of double tapered roller R along the generator of conical or tapered surfaces Ra, Rb is 4.8 mm, the length l1 of corners Rc, Rd is 0.5 mm, and the apex angle xcex8 is 90xc2x0, by applying a thrust load to the bearing by 50 kgf per piece of double tapered rollers, the edge load occurring at the small end side of the section straight line is known to reach about 500 kgf/mm2.
The invention is devised in the light of such problems of the prior art, and it is hence an object thereof to present double tapered rollers having a structure of assuring an appropriate contact stress with the bearing races, without causing edge load due to load at both ends of the section straight line on the conical surfaces.
To achieve the object, the double tapered roller of scroll thrust bearing of the invention is characterized in that a conical body has a pair of conical or tapered surfaces matched coaxially and coupled at bottoms mutually, and the entire surface of the pair of conical surfaces is processed by crowning.
In a preferred embodiment, the outer contour shape of the crowning is an arc shape having a single radius of curvature along the overall length of the generator of the conical surface, and the radius of curvature of the arc shape is set at 100 times or less of the generator length of the conical surface.
The invention is based on the results of various preceding tests and studies by the present inventor.
First, the inventor noticed that the cylindrical surface of the cylindrical roller was generally processed by crowning hitherto in order to prevent generation of edge load due to load at both ends of the section straight line (generator) (for example, Japanese Laid-open Patent No. 59-69519, Japanese Laid-open Utility Model No. 2-141723, Japanese Laid-open Patent No. 4-60215).
That is, as shown in FIG. 6, the conical or tapered surfaces Ra, Rb of the double tapered roller R were processed by crowning C1, C1 same as in the cylindrical surface of cylindrical roller. In this shape, however, generation of edge load at both ends of the section straight line (generator) was eliminated, but the tendency of increase of contact stress at the apex side was not improved.
For example, in FIG. 6, in the case of the length L of the double tapered roller R along the generators of the conical surfaces Ra, Rb of 4.8 mm, the length l1 of the corners Rc, Rd of 0.4 mm, the length l2 of crowning C1 of 0.2 mm, and the apex angle xcex8 of 90xc2x0, when a load of 50 kgf was applied per piece of double tapered rollers, the maximum contact stress at the small end side of the section straight line was found to reach about 300 kgf/mm2 (the allowable maximum contact stress being 250 kgf/mm2)
On the basis of such results, further tests and studies were continued, and the invention having such constitution is realized.
In the invention, since the entire surface of the pair of conical or tapered surfaces is processed by crowning, that is, full-crowning is processed, edge load is not generated at both ends of the section straight line of the conical surfaces, and the contact stress at the apex side can be suppressed to a low value within an allowable range.